The Met has said the Barclays gang ran an much more sophisticated operations and arrests include a suspect police are calling the 'Mr Big' of UK cybercrime.

"These arrests form part of a covert operation designed to tackle major cyber-led crime. We believe that someone had posed as an engineer to enter the Swiss Cottage branch of Barclays and had managed to fit a device which gave them remote access to their computers. With this remote access they could siphon off cash from customer accounts," said detective superintendent Terry Wilson.

"This was a highly-organised criminal network with each individual filling a specific role. All criminal networks have a head and we very much believe we have now apprehended our 'Mr Big' as part of this operation. We believe this has put a major dent in this alleged criminal network's ability to commit cybercrime in this country," he added.

Searches are currently being carried out at addresses across London and Essex. Property including cash, jewellery, drugs, thousands of credit cards and personal data has been seized.

A central London house in Westminster has been described by detectives as the "control centre" from which the fraudsters operated.

The men, aged between 24 and 47, remain in custody after being arrested on Thursday and Friday.

Barclays were able to recover a significant amount of the funds stolen, police have said.